This invention relates, in general, to a motion signal processing system for digital televisions. In particular, the present invention relates to a circuit for smoothing image signals distributed in a boundary region of a motion image and a still image by spreading the transition between the two regions, in which the circuit re-constructs the temporally processed motion signal into a spatially processed motion signal.
A digital video signal processing system, which is widely researched recently, uses large memories and, in this case, in order to obtain a good quality displayed image, the digital video signal processing system frequently uses frame memories. The video signal processing system utilizing frame memories uses the comb-filters so as to easily separate the luminance signals and the chrominance signals from composite video signals. These comb-filters work well for the still images which do not contain image motion. However, it is a disadvantage of the above technique that, around motion areas, distortion appears which greatly reduces the quality of the displayed image.
In order to avoid such degradation of the image near motion, it becomes necessary to switch from the frame combed signal to some kind of substitution signal that provides a better quality than the frame combed signal. By the way, there are proposed two methods for achieving the switching operation between the two signals, i.e., one is a hard switching and the other is a soft switching technique.
The hard switching, as the result of the motion detection, has only two states (1; motion area, or 0; still area) with no intermediate states. Therefore, when this hard switching is employed, a new degradation of the displayed image will be incurred. This degradation of the image is basically caused by the difference in resolution between the frame combed signal and the substitutional signal of better quality. Another very noticeable distortion appears when the substitution signal consists of a line combed signal. In this case, hanging dots appear along moving horizontal transitions.
This distortion becomes especially annoying when the image contains a lot of moving high frequency detail, and the system therefore rapidly switches between two differently processed signals.
Therefore, for a digital video signal processor, it is desirable to have a soft switch which provides gradual transitions between moving and stationary portions of the picture. A general motion signal processing system for implementing this soft switching is as schematically shown in FIG. 1.
Referring to FIG. 1, it is an exemplary illustration of a 1-bit motion signal spreader. However, for a full bit motion signal processing, the motion detector 100 and control signal spreader 102 should respectively be replaced by a motion detector for producing full bit motion signals and a K value generator for generating K values of 0 to 1.
Namely, as shown from the drawing, a general motion signal processing system includes essentially the motion detector 100 for detecting motion signals from the composite video signal input, and the control signal spreader 102 for processing the motion signals provided from the motion detector 100 so as to generate the spread control signal of K and 1-K values. Furthermore, a spatial processor 106 spatially processes the composite video signal input by using line comb-filters and a temporal processor 110 temporally processes the composite video signal input by using frame comb-filters. The respective outputs of the spatial processor 106 and the temporal processor 110 are mixed with the control signal output of K value and 1-K value provided from the control signal spreader 102 by virtue of multipliers 112 and 114, respectively. In this case, the control signal is of 0&lt;K&lt;1. The respective outputs of the multipliers 112 and 114 are mixed by a adder 116 to produce motion processed image signals. Since the composite video signal input is delayed during processing by the motion detector 100 and the control signal spreader 102, delay circuits 104 and 108 delay the composite video signal input in order to match control signal K and 1-K values with the outputs of the spatial processor 106 and the temporal processor 110.
Referring to FIG. 2, it is a block diagram for showing the structure of the motion detector 100 and the control signal spreader 102 according to a prior art, in which a frame difference circuit 118 receives the composite video signal or luminance signal and detects a motion difference signal between frames. A spatial low pass filter 120 spatially lowpass-filters the frame difference signal provided from the frame difference circuit 118 so as to smooth the motion difference signal and restrict the color signal. An absolute value circuit 122 produces absolute values of the signal output from the spatial lowpass filter 120. The absolute values are compared with a predetermined threshold value by a comparator 124 which generates the 1-bit control signal according to the comparison. Then, the 1-bit control signal is spread by a spreading processor 126 and the K values are then generated by the K value generator 132. Herein, the K values have continuous values of 0.ltoreq.K.ltoreq.1 when a K value is 1, the motion of image is very significant and when the K value is 0, the motion of image is none.
Since this prior art motion signal processor forcefully performs the spreading process centering around a detected motion signal, regarding the detected 1-bit motion signal as a motion signal (K=1) of which motion is very considerable, the motion signal can not be spread adaptively. Accordingly, when a lot of moving high-frequency detail is processed, the degradation of the displayed image can not be avoided successfully. Furthermore, when image signals contain impulse noise, the impulse noise may be misconceived as motion signals and thus spreading of undesired image signals occurs. In addition, since this structure detects only motion signals correlated to the direction of time axis in accordance with only the frame difference signal, the motion signal has little spatial correlation. Therefore, it is difficult to process the motion signal spatially adaptively according to the motion area.